As is to be appreciated, in numerous situations, the presence of background acoustic noise is undesirable for a physician attempting to listen to a heartbeat or systolic murmur from a rapid heart beat of a patient to make an immediate determination or diagnosis of the patient's condition. As an example, consider the situation in which a doctor or paramedic is trying to listen with the use of a stethoscope to a heart rate of a sick person to determine the heart condition of the individual in an ambulance with a siren blaring.
In this situation, loud acoustic background noise from the siren or from any other ambient noise in the vicinity is received in a standard microphone, usually a omnidirectional microphone, located in the stethoscope housing. The noise and the sound signal are then converted to an electrical signal by the circuitry contained within the housing of a standard stethoscope. The electrical signal is then amplified and supplied to the ear of the attendant checking out the condition of the patient and is converted thereat to an acoustic signal. This resulting signal is a distorted reading of the patient's heart rate as background noise is include in the sound conveyed to a physician's ear or to a computer recording the sound of the heart rate.
As a result, the physician fails to obtain an accurate reading of the patient's heart rate because of the transmission of background noise, when utilizing a conventional stethoscope in an ambulance or noisy emergency room. Even more critical a situation is when a person has suffered a heart attack and a correct reading of the heart attack patient's heart rate could mean life or death in the next step to save the person's life. Moreover, the sound of the heart combined with the background noise may make it difficult for the doctor or nurse to monitor the heart rate to determine whether shock treatment is necessary.
Conventional or state-of-the art stethoscopes, such as the Analyst available from Heartsounds in Ontario, Canada, do not reduce or cancel background noise to improve performance of stethoscope utilized in a noisy environment or the like. Rather, the standard microphone utilized in such conventional stethoscopes are omnidirectional microphones. These standard microphones accept background and sound signals and convey an electrical signal, which is degraded by ambient noise to the electrical processing means within the stethoscope. Furthermore, an omnidirectional microphone accepts signals in all directions, including ambient noise propagating in more than one direction which is transmitted as an input signal to the microphone together with the sounds obtained from listening to the heart.
Thus, the utilization of the omnidirectional microphone in the standard stethoscope does not prevent heart sounds, especially at low frequencies, from being distorted in a noisy environment or when utilizing digital means to convey sound signal when using stethoscope. Support that the heart rate sounds are distort when using omnidirectional microphones in stethoscopes is shown in the comparative testing performed by Andrea Electronics Corporation of an Analyst stethoscope and a stethoscope made in accordance with the present invention.
For instance, the Analyst stethoscope at low frequencies that are under 1 kHz detects or picks up unwanted background noise when processing the digital heart rate received from the patient in a noisy environment, which in turns degrades the heart rate calculation. Furthermore, the Analyst is used in connection with computer software that samples the heart rate at low frequencies or at narrower bandwidths. Therefore, it is desirable to cancel noise before it is transmitted to the software sampling to prevent an inaccurate software heart rate sampling.
Conventional omnidirectional microphones located in prior art stethoscopes cannot simply be replaced with noise canceling microphones having pressure sensitive surfaces with a low gain to enhance noise canceling without typically having to reconfigure the entire stethoscope. Simple replacement of the type of microphone does not solve the problem. Rather, as will be discussed in the present invention, the mechanical/acoustical arrangement of the microphone within the necessary input ports of the microphone isolator acoustic coupler must take place so that noise cancellation occurs. This is because the mechanical/acoustical arrangement of the noise canceling microphone allows for sound equalization of the noise received from the noise port to achieve performance in calculating the number of beats per minute of the patient's heart, as such, would be relatively expensive.
Thus, the prior art has failed to provide a relatively low-cost means for reducing or canceling background noise to achieve an accurate heart rate of a patient by mechanically/acoustically diffraction means, and a cost-effective means for enabling existing stethoscope that does or does not use digital network to sample heart rates by computer means or manually by listening and recording the rate on the patient's chart.